1. Field of the Invention
This invention relates to a surface optical device apparatus which can be optically coupled to a light-transmission member, such as an optical fiber, readily and effectively, an optical apparatus which includes the surface optical device apparatus and a light-transmission member optically coupled to this surface optical device apparatus accurately and effectively, its fabrication method, an optical wiring device using the optical apparatus, and related structures and devices. The surface optical device apparatus and optical apparatus are also referred to as an optical interconnection module or the like in this specification.
2. Related Background Art
In recent years, an optical module for fast optical interconnection has been developed. However, there are a number of problems concerning the connection between the optical module and an optical device or a light-transmission member, such as an optical fiber, particularly from the standpoint of cost and performance.
A surface device is chiefly used as a light-receiving device among optical devices since this is advantageous in fabrication ease and sensitivity. In this case, when a principal surface of the surface device is to be coupled to an optical fiber at a relatively low cost, the surface device needs to be passively aligned with the optical fiber while not in operation. For this purpose, a method of assembling the devices with a fixing member is ordinarily employed. In such a case, however, mechanical precision of the fixing member is required, there exist limitations with respect to its elastic coefficient and thermal expansion efficient, and the number of components increases. Hence, a decrease in cost is difficult. Particularly, where plastic molding is used to reduce the cost, yield and long-term reliability in the optical coupling are lowered.
With a light-emitting device also, a vertical cavity surface emitting laser (VCSEL) for emitting light perpendicularly to its substrate face is being energetically researched and developed, as the VCSEL has a possibility of reducing power consumption and cost of an optical interconnection module. In VCSEL, its threshold is low (approximately less than 1 mA), inspection on a wafer level is possible, and no cleavage precision is needed. Its cost can be thus lowered. However, in an optical coupling between such a laser and an optical fiber also, the problems similar to the above still exist.
In the above-discussed situation, there has been proposed a method of forming a fiber guide hole for coupling an optical device to an optical fiber with a precision of photolithography. For example, Japanese Patent Application Laid-Open No. 8(1996)-111559 discloses a method of etching a hole for fixing an optical fiber 1037 to the side of a substrate 1021 with a surface light-receiving or light-emitting device, as illustrated in FIG. 1. In FIG. 1, there are also illustrated a light absorbing layer 1022, distributed Bragg reflector (DBR) mirrors 1023 and 1027, cladding layers 1024 and 1026, an active layer 1025, a contact layer 1028, an SiO2 layer 1032, electrodes 1033 and 1035, and an anti-reflection film 1036.
Further, Japanese Patent Application Laid-Open No. 6(1994)-237016 discloses a method of fixing an optical fiber 1210 in a fiber guide hole 1209 etched in a substrate of a surface emitting laser 1203, as illustrated in FIG. 2. In FIG. 2, there are also illustrated an electronic circuit substrate 1201, a light-emitting chip 1202, a transistor 1204, transistor electrodes 1205, 1206 and 1207, an insulating layer 1208, and an adhesive 1211.
In those prior art methods, the number of components can be reduced, assemblage is very easy, and costs can be hence reduced. However, in the former prior art method (FIG. 1), it is difficult to control the distance between the optical fiber and the light-receiving or light-emitting portion, and there is a possibility of damaging the crystal upon impinging the optical fiber on the crystal and degrading the device. Therefore, in the latter prior art method (FIG. 2), the guide hole 1209 is tapered to decrease the diameter of its tip portion such that the optical fiber 1210 cannot be brought into contact with the crystal surface, and the substrate is not completely etched down to epitaxial layers such that a substrate portion slightly remains.
On the other hand, there has also been proposed a method of fixing a member for fixing an optical fiber directly to the surface of a substrate with surface optical devices. For example, Japanese Patent Application Laid-Open No. 11(1999)-307869 discloses a structure as illustrated in FIG. 3. In FIG. 3, protrusions 2022 and 2023 are formed on surface emitting lasers 2018, a member 2014 for fixing an optical fiber 2016 is fitted into the protrusions 2022 and 2023, and guide holes 2026 and 2027 are formed in the member 2014 at a position corresponding to a radiation portion of the laser 2018. In FIG. 3, there are also provided a module substrate 2012 and a hole 2024 for inserting the optical fiber 2016 therein.
In forming the fiber guide hole by etching, however, control of its tapering shape and hole diameter is Questionable, since its depth ordinarily reaches more than 100 μm. It is thus difficult to improve the yield. Further, where a portion of the substrate is left (FIG. 2), there occurs the problem that light is absorbed by this portion, and hence, usable wavelength of light is restricted.
When the block for fixing an optical fiber is used (FIG. 3), fabrication costs can not be necessarily lowered since the numbers of components and process steps increase, though the fabrication problems mentioned above can be solved.
Furthermore, an optical fiber is required to be positioned as closely as possible to a light-receiving device since light emerging from the end face of the optical fiber expands. It is, however, difficult to increase an incidence efficiency of light input into the light-receiving device. Similarly, it is hard to increase an optical coupling efficiency between light from a light-emitting device and an optical fiber, when a mismatch is large between radiation diameter and radiation angle of the light-emitting device and core diameter and reception angle of the optical fiber.